Defense Technology International - March 2007 - (Page 10)
SCIENCE WATCH MICHAEL DUMIAK TRIGGER EFFECT Almost half of American deaths
in Iraq last year were caused by improvised explosive devices IEDs . The
same low-tech weapons, most drawn from a seemingly limitless stock of
looted Iraqi army ordnance, also killed thousands of civilians caught in
the crosshairs of sectarian violence. These weapons are set off remotely,
using electronic detonators activated by signals from a range of everyday
consumer electronics—mobile phones, garage-door openers, remote controls
for toys, motion detectors, infrared camera flash sensors. The Pentagon has
fielded numerous jamming devices in Iraq for some time, but the IEDs keep
exploding. This raises a number of perplexing questions, the main one
being why it is so hard to pinpoint and block electronic signals from cell
phones and other common devices. The wired U.S. military faces an enemy
that has become proficient at creating and using its own electronic
networks, however unsophisticated, to disrupt operations, often with
deadly consequences. Disposable cell phones, anonymous Internet cafes and
ad hoc websites are potent weapons in the hands of insurgents. But with
advanced technology part of the military’s DNA, is it possible, despite
the density, speed and variety of electronic signals passing through the
ether, to create a “bubble of silence,” a moving, airtight, protected
zone that stops all IEDtriggering signals? “It is possible,” says Gerd
Wollmann, Rheinmetall’s head of development for nonlethal weapons. But
from a scale beginning at zero—complete spectrum lockdown—problems
start by allowing spaces in electromagnetic frequencies for legitimate
communication needs. Wollmann says radio-frequency jammers leave uncovered
gaps in the spectrum and can be predictable. Consider that each base
station in a mobile phone system has 170 channels available for use at any
time, and that those channels can be repeated at nearby stations.
“[Insurgents] know which frequencies the troops are jamming. It’s
simple to use a mobile phone and call your colleague 2 km. 1.2 mi. away
and tell him: ‘Don’t use this frequency, use that instead.’” To
stop signals in the electromagnetic spectrum, all that must be done is
produce a stronger signal at the same frequency. If the enemy is using a
garage door opener, a sine wave at that frequency could stop it. But if
the exact frequency isn’t known, it becomes difficult. Jamming all
freRHEINMETALL Rheinmetall is working on technology that uses
ultra-wideband impulses covering the frequency spectrum from a few
megahertz to 3 GHz. quencies requires a lot more technology. Either
several emitters and antennas are used to cover the spectrum, or something
very broadband must be generated. The way to do this is with short pulses
and a high repetition rate—the shorter the pulse, the larger the
spectrum covered. Science in the field is opaque as many experts operate
in the shadows. The Defense Dept.’s Joint Improvised Explosive Device
Defeat Organization, which has caught flak for its multibillion-dollar
efforts in the area, didn’t return calls. The Pentagon has said its use
of frequencyband jammers, like Warlock from EDO Corp. and Raytheon's ICE
IED Countermeasure Equipment , is reducing the number of casualties per
attack. About 7,000 jammers are reportedly deployed. Still, the attacks
are increasing, casualties persist and research efforts are
intensifying— some $6 billion is slated for R&D in the current Pentagon
budget request. Wollmann’s team thinks it’s on to something using
high-power microwave pulses from a mountable suit- case-sized emitter. The
microwaves trigger sensor-rigged improvised bombs about 30 meters 98 ft. in
front of a speeding vehicle. Microwaves are relatively short in the
electromagnetic spectrum compared to radio waves. When stacked in very
quick pulses, they make a broadband sweep, blocking signals ranging from a
few megahertz to 3 GHz.—everything from garage-door openers 20-30 MHz. to
mobile phones 800-900 MHz. and 1800-1900 MHz. and wireless local area
networks 2.4 GHz. . “And we know exactly when our pulses come,”
Wollmann says. “So you can, in a way, communicate in between them.”
It’s possible to synchronize pulses with picosecond accuracy. If systems
can be tuned with this in mind, the military would have a lockdown system
with communication capability. For now, however, it remains to be seen.
Rheinmetall’s gear is production-ready, but will take some time to get
into the field in Iraq or Afghanistan, even assuming contracts come
through. Meanwhile, Clemson University engineer Todd Hubing has been
working a different angle. Everything with a microprocessor in it produces
a small amount of electromagnetic radiation. He’s working on algorithms
that would sort the massive electronic noise of an urban environment into
recognizable patterns and show where the radio receiver of a bomb is
located. “When we started this project, we were sure we could identify
devices based on their unintentional emissions. We’d been doing that for
a long time,” Hubing says. The auto industry is concerned that radio
waves don't interfere with the computers and electronics in cars, and
Hubing’s diagnostic engineering work for auto companies in the past had
been in the cause of dampening electromagnetic emissions. Why not just
unplug the mobile phone system in Baghdad? The time for that is probably
past—it gets lost these days, but one objective is to build
infrastructure in Iraq, not shut it down. “And that would just disable
mobile phones. It wouldn’t disable all the other things that are being
improvised,” Hubing says. ■ www.aviationweek.com/dti 10 DEFENSE
TECHNOLOGY INTERNATIONAL MARCH 2007
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